XVI International Botanical Congess

Differential growth leading to negative gravitropic curvature in Pellia sporophytes was studied using infrared video recordings. After horizontal placement, rates on the top side of sporophyte stalks drop from 0.53 to 0.29 mm/hour, and rise to 0.88 mm/hour on the bottom. Laterally applied auxin also influences growth, with a 10-6 M peak. Preliminary results from tracer experiments suggest that lebeled auxin moves laterally through stalks in response to gravity. Starch granules in stalk cells also settle quickly in response. These observations are consistent with 1) a mechanism for gravitropic mediation that involves lateral redistribution of auxin (a.k.a. the Cholodony-Went hypothesis), and 2) detection of gravity by starch statoliths.